Current sensing apparatus

ABSTRACT

This application relates to a fan control apparatus for actuating a fan to circulate air over a plurality of electric environmental change elements included in a temperature control system. The apparatus includes a fan in circuit with switch means which is operative in response to an electrical signal to actuate the fan. A sensing element is disposed in electrically inductive relationship with the environmental change elements and is responsive to energization of any one of such elements to generate said electrical signal and effect closing of the switch means to actuate the fan. The signal will continue and maintain the fan operative as long as the environmental change elements are energized and will be rendered inoperative when the last change element is de-energized thus discontinuing said signal and deactuating said fan.

United States Patent Chambers [54] CURRENT SENSING APPARATUS [72]Inventor: William W. Chambers, Anaheim, Calif.

[7 3] Assignee: Robertshaw Controls Company,

Richmond, Va.

[22] Filed: Mar. 3, 1969 [21] Appl. No.: 814,491

Related U.S. Application Data [63] Continuation-impart of Ser. No.774,863, Nov. 12,

1968, abandoned.

[52] U.S.Cl ..317/148.5 B,307/l3l,307/154, 219/476, 219/497, 219/501,3l7/DlG. 5 [51] Int. Cl ..l-l0lh 47/32, l-l05b 3/02 [58] Field ofSearch..3l7/l37, 148.5 B; 307/131, 307/154; 219/476, 497, 501

[56] References Cited UNlTED STATES PATENTS 3,329,869 7/1967 Obenhaus..3l7/l48.5 B

[ 51 Apr. 25, 1972 3,419,756 12/1968 Philibert et al ..317/l48.5 B

Primary Examiner-L. T. Hix Attorney-Fulwider, Patton, Rieber, Lee &Utecht [57] ABSTRACT This application relates to a fan control apparatusfor actuating a fan to circulate air over a plurality of electricenvironmental change elements included in a temperature control system.The apparatus includes a fan in circuit with switch means which isoperative in response to an electrical signal to actuate the fan. Asensing element is disposed in electrically inductive relationship withthe environmental change elements and is responsive to energization ofany one of such elements to generate said electrical signal and effectclosing of the switch means to actuate the fan. The Signal will continueand maintain the fan operative as long as the environmental changeelements are energized and will be rendered inoperative when the lastchange element is de-energized thus discontinuing said signal anddeactuating said fan.

7 Claims, 2 Drawing Figures Patented April 25, 1972 INVENTOR W/LL/AM MI.fi/mMae-las BY W Amen/ms CURRENT SENSING APPARATUS This application is acontinuation-in-part of Ser. No. 774,863, filed Nov. 12, 1968, and nowabandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to fan control devices which are utilized to force airin heat exchange relationship with an environmental change device.

2. Description of the Prior Art It has been common practice to sensecurrent conduction in an electrical lead to carry out variousoperations, such as energization of a load. However, applicant isunaware of any prior art current sensing control apparatus which sensesthe current conduction in a lead and amplifies the sensed signal to firea gate controlled switching device.

SUMMARY OF THE INVENTION The present invention is characterized bytrigger means disposed in electrically inductive relationship with anelectrical lead and responsive to a predetermined magnitude of currenttherein to generate a signal for operating a switch in a load circuit.

The objects and advantages of the present invention will become apparentfrom the consideration of the following detailed description when takenin conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of a fan controlapparatus embodying the present invention; and 7 FIG. 2 is amodification of the fan control apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The fan control apparatus shownin FIG. 1 may be conveniently utilized to force air over a plurality ofparallel connected environmental heating elements 11, 13, 15, 17 and 19which are connected in series with respective time delay switches 21,23, 25, 27 and 29; A ferro-magnetic current sensing core, generallydesignated 33, encircles the leads to the switches 21, 23, 25, 27 and 29and has an amplification coil 35 wrapped on one leg thereof forproviding a triggering signal on the gate of a controlled switch meansin the form of a silicon controlled rectifier (SCR) 37 whenever any oneof the such switches are closed to thereby energize a relay, generallydesignated 39, and actuate blower fan 41 to circulate air over theheaters 11, 13, 15, 17 and 19 and continue such circulation until allthe switches 21, 23, 25, 27 and 29 are opened.

Each of the delay switches 21, 23, 25, 27 and 29 are driven byrespective bimetalic blades 51, 53, 55, 57 and 59. Movement of suchblades toward the switch closed position is restricted by respectivesnap-acting springs 61, 63, 65, 67 and 69, which springs have thecharacteristics of providing a bias to resist closure of the bladesuntil a predetermined force is applied thereto, at which point the biasof such springs is overcome and they relieve to permit rapid closure ofthe respective switches.

Current to the environmental heating heating elements 11, 13, 15, 17 and19 is provided by power leads 71 and 73. A transformer, generallydesignated 75 has its primary coil 77 connected between the leads 71 and73. A heat motor 79 encircles the first stage blade 51 and is connectedacross the secondary coil 81 of the transformer 75 by means of a lead 82having a control switch 83 therein. The control switch 83 is coupledwith a thermostat 84 which is responsive to changes in the environmentaltemperature to effect closure of such switch 83.

The switch 21 is connected between the leads 71 and 73 by means of leads85, 87, 89, the second stage blade 53 and a limit switch 91. Similarlythe switch 23 is connected between the power leads 71 and 73 by means ofleads 95, 97, 99, the blade 55, and a limit switch 101; the switch 25 byleads 105, 107, 109, the blade 57 and limit switch 111; the switch 27 byleads 115, 117, 119, blade 59 and limit 121; and the switch 29 by meansof leads 125, 127, 129 and a limit switch 131.

The blower fan 41 is connected between the leads 71 and 73 and isconnected in series with the switch 131 of the relay 39, The coil 133 ofthe relay 39 is connected across the secondary coil 81 of thetransformer 75 by means of leads 135, 137 and 139. The load circuit ofthe SCR 37 is connected in series between the transformer coil 81 andthe relay coil 133 to control current flow therebetween, the gate ofsuch SCR being connected with the amplication coil 35 by a lead 134.

Connected across the relay coil 133 is a free-wheeling diode 141 todirect current flow through the coil 133 during positive going halfcycles and to, itself, provide a path for current flow during negativegoing half cycles to eliminate hum and prevent voltage build up in thecoil 133.

A capacitor 142 is connected across the secondary coil 81 of thetransformer 75 to absorb momentary current surges resulting from closureof the switch to thereby prevent imposition of such current on the anodeand cathode of the SCR 37 to cause triggering thereof.

In operation, the thermostate 83 is set at the desired environmentaltemperature and when the temperature falls below the selected level, theswitch 83 will be closed to provide current to the heat motor 79 of thefirst stage switch 21. As noted above closure of the switch 83 willcause a momentary surge of current from the secondary coil 81 which willbe absorbed by the capacitor 142 to prevent the SCR 37 from beingtriggered by its cathode being driven sufficiently far negative relativeto its gate or its anode being driven sufficiently far positive relativeto its gate to cause triggering. After a selected period of time, themotor 79 will heat the first stage blade 51 sufficiently to cause itsupper end to flex to the right and overcome the bias of the spring 61causing such spring to relieve and snapping the switch 21 closed.Closure of the switch 21 provides current through the blade 53 of thesecond stage switch 23 and through the first stage heating element 11.

Current flow through the lead to the first stage switch 21 induces amagnetic field around such lead, which field is concentrated in therectangular core 33 thus inducing current flow in the sensing coil 35.Current in the coil 35 will be conducted to the gate of the SCR 37 bythe lead 134 thus triggering such SCR and providing for current fiowfrom the secondary coil 81 of the transformer 75 to the coil 133 of therelay 39. Energization of the coil 133 effects closure of the switch 131to energize the fan 41 thus assuring immediate circulation of air overthe energized resistance heater 11 to prevent overheating thereof.

A predetermined time after closure of the switch 21 and commencement ofcurrent flow through the blade 53 of the second stage switch 23, suchblade will flex to overcome the bias of the spring 63 and effect snapclosing of the switch 23 thereby commencing current flow through thethird stage blade 35 and second stage resistant heater 13. A selectedperiod of time thereafter such blade 55 will flex to close the thirdswitch 25 thereby energizing the fourth stage blade 57 and the thirdstage heating element 15. Subsequently, the fourth stage switch 27 willbe closed and, thereafter, the fifth stage switch 29 will be closed in alike manner.

Under normal conditions, the heat generated from the heating elements11, 13, 15, 17 and 19 and circulated by means of a fan 41 will heat theenvironment sufficiently to cause the thermostat 84 to open the switch83 thus discontinuing current to the heat motor 79 of the first stageswitch 21. The first stage blade 51 will then cool and be snapped openby the spring 61 to discontinue current flow through the first stageheating element 11. Opening of the switch 21 will likewise discontinuecurrent flow through the second stage blade 33 thus opening the secondstage switch 23 and discontinuing current flow through the third stageblade 55 and the second stage heating element 13. The remaining switches25, 27 and 29 will likewise be opened in sequence and when the laststage switch 29 is opened to discontinue current flow through the lead125 connected therewith, current from the sensing coil 35 to the gate ofthe SCR 37 will be discontinued rendering such SCR non-conductive andde-energizing the coil 133 of the relay 39 to open the fan switch 131and discontinue operation of the fan 41.

It is of particular importance that the fan control is operativewhenever any one of the switches 21, 23, 25, 27 or 29 is closed toprovide air circulation over the energized heat element l1, l3, 15, 17or 19 to prevent overheating thereof. The fact that the leads to eachone of the switches 21, 23, 25, 27 and 29 is sensed will assureoperation of the fan even in the case of temporary loss of power andsubsequent application thereof whereeach of the blades 51, 53, 55, 57and 59 will commence cooling simultaneously when power is lost and willopen in accordance with the time constant for the particular blade and,when the power recommences, if, for example, the switch 25 is the onlyone closed the fan 41 will still be operated to maintain the element 15cooled.

While the triggering element has been described as an SCR, obviously atriac could be substituted therefore.

The modification shown in FIG. 2 includes a resistor 152 which issubstituted for the diode 141 shown in FIG. 1 to thus partially blockcurrent flow during forward going half cycles to direct a portion ofsuch current through the coil 133 and to, itself, form a path for flowof current induced by decay of the field around the coil 133 duringnegative going half cycles.

From the foregoing it will be apparent that the fan control system ofpresent invention is straight forward in design and economical tomanufacture. The control apparatus will provide a long and service-freeoperational life and will insure operation of the fan whenever any oneof the heating elements are energized. Also, since the sensor coil iselectrically isolated from the leads to the respective heating elements,the fan relay may be operated from the power leads as well as from thesecondary coil of the transformer.

Various modifications and changes may be made with regard to theforegoing detailed description without departing from the spirit of theinvention.

lclaim 1. Current sensing control apparatus for operation of anelectrical load circuit and comprising:

gate controlled switch means for controlling current in said loadcircuit;

a plurality of switches;

electrical leads connected with said switches and leading to separateelectrical elements;

time delay means for actuating said switches at different times;

current sensing means inductively coupled to said electrical leads andresponsive to current flow in any one of said electrical leads toproduce an electrical signal; and

amplification means electrically coupled to said sensing means and tothe gate of said switch means and operable to receive said electricalsignal and amplify it to produce said triggering signal whereby currentflowing in any one of said electrical leads will be sensed by saidsensing means to produce said electrical signal and said amplificationmeans will amplify said signal to impose said triggering signal on saidgate to trigger said switch means and operate said load circuit.

2. Current sensing control apparatus as set forth in claim 1 wherein:

said sensing means includes a ferromagnetic core; and

said amplification means includes coil means wound on said core.

3. Current sensing control apparatus as set forth in claim 1 thatincludes:

capaticance means connected with the gate of said switch means to absorbcurrent surges introduced thereto to prevent accidental actuation ofsaid switching means.

4. Current sensing control apparatus as set forth in claim 1 wherein: I

said electrical elements are in the form of resistance heating elements.5. Current sensing control apparatus as set forth in claim 1 wherein:

said electrical elements are in the form of temperature change element;and said load circuit includes fan means responsive to operation of saidload circuit to circulate fluid in heat exchange relationship with saidtemperature change elements whereby said fan means will be operatedwhenever any of said temperature change elements is energized to therebyprevent said temperature change elements from reaching excessivetemperature. 6. Current sensing control apparatus as set forth in claim1 wherein:

said electrical elements are in the form of heating elements;

and said load circuit includes fan means responsive to operation of saidload circuit for circulating fluid in heat exchange relationship withsaid heating elements whereby said fan means will be actuated whenevercurrent is conducted in any one of said electrical leads. 7. Currentsensing control apparatus as set forth in claim 5 that includes:

thermostat means for sensing the temperature of the fluid circulated inheat exchange relationship with said temperature change elements andconnected with said temperature change elements, said thermostat beingresponsive to the temperature of said fluid falling outside apredetermined range to actuate said temperature change elements.

1. Current sensing control apparatus for operation of an electrical loadcircuit and comprising: gate controlled switch means for controllingcurrent in said load circuit; a plurality of switches; electrical leadsconnected with said switches and leading to separate electricalelements; time delay means for actuating said switches at differenttimes; current sensing means inductively coupled to said electricalleads and responsive to current flow in any one of said electrical leadsto produce an electrical signal; and amplification means electricallycoupled to said sensing means and to the gate of said switch means andoperable to receive said electrical signal and amplify it to producesaid triggering signal whereby current flowing in any one of saidelectrical leads will be sensed by said sensing means to produce saidelectrical signal and said amplification means will amplify said signalto impose said triggering signal on said gate to trigger said switchmeans and operate said load circuit.
 2. Current sensing controlapparatus as set forth in claim 1 wherein: said sensing means includes aferromagnetic core; and said amplification means includes coil meanswound on said core.
 3. Current sensing control apparatus as set forth inclaim 1 that includes: capaticance means connected with the gate of saidswitch means to absorb current surges introduced thereto to preventaccidental actuation of said switching means.
 4. Current sensing controlapparatus as set forth in claim 1 wherein: said electrical elements arein the form of resistance heating elements.
 5. Current sensing controlapparatus as set forth in claim 1 wherein: said electrical elements arein the form of temperature change element; and said load circuitincludes fan means responsive to operation of said load circuit tocirculate fluid in heat exchange relationship with said temperaturechange elements whereby said fan means will be operated whenever any ofsaid temperature change elements is energized to thereby prevent saidtemperature change elements from reaching excessive temperature. 6.Current sensing control apparatus as set forth in claim 1 wherein: saidelectrical elements are in the form of heating elements; and said loadcircuit includes fan means responsive to operation of said load circuitfor circulating fluid in heat exchange relationship with said heatingelements whereby said fan means will be actuated whenever current isconducted in any one of said electrical leads.
 7. Current sensingcontrol apparatus as set forth in claim 5 that includes: thermostatmeans for sensing the temperature of the fluid circulated in heatexchange relationship with said temperature change elements andconnected with said temperature change elements, said thermostat beingresponsive to the temperature of said fluid falling outside apredetermined range to actuate said temperature change elements.